Electrostatic printing apparatus using charge induced toning

ABSTRACT

A source of electrostatic charges comprising a latent electrostatic image is brought into close proximity to a record member having one face of the said record member wetted by a liquid toner. The toner is in contact with both the electrostatic charge source and the record member for an interval during which a latent charge of opposite sign is induced in the record member and the toner particles in the liquid toner are driven by the field lines established between the electrostatic charge source and the induced charge on the record member to form a visible image on the record member.

United States Patent 1191 Robinson et al. 96/l .4

' Kaufman Dec. 17, 1974 [5 ELECTROSTATIC PRINTING APPARATUS 3,705,768 12/1972 Moravv etal 355/8 USING CHARGE INDUCED TONING FOREIGN PATENTS OR APPLICATIONS. [76] Inventor: Arthur L. Kaufman, 26 High Point 27,558 0/1969 Japan 355/l0 Rd., Westport, Conn. 06880 Sept. 10, Primary Examiner -Rlchard Moses 21 App]. 1516.; 395,525 57 ABSTRACT Related US. Application Data ,A source of electrostatic charges comprising alatent [63] Continuation f s NO. 221,646, J 28,1971 electrostatic image is brought into close proximity to a record member having one face of the said record 52 US. Cl. 355/10, 96/1 LY, 117/37 LE, member wetted y a liquid toner- Themner is in 118/DlG 23 3 55/16 contact with both the electrostatic charge source and [51] Int. Cl. 603g 9/04, G03g 13/10 the record member for interval during which a [58] Field of Search 355/10, l6, 17; 96/1 LY; n Charge of Opposite Sign is induced in the record 1 17 37 1 13 23 member and the toner particles in the liquid toner are driven by the field lines established between the elec- [56] References Ci trostatic charge source and the induced charge on the UNITED STATES PATENTS I record member to form a visible image on the-record 1 1 1 member. 3,28l,24l 10/1966 MlhfijlOV 96/1 3,556,784 1/ I971 16 Claims, 4 Drawing Figures A ELECTROSTATIC PRINTING APPARATUS the toner liquid. (which are of opposite sign from the Electrostatic printing apparatus in which a latent charge image is formed upon a surface suchas photo- Q conductive insulating layer, toned by theapplication of member. The toning of the record memberduring the induction charging of the record member is herein re- 7 fer'red to as indu c tion toning. 1

The toned record member is next separated from the. latent image bearing member following which it may be dried in air or squeegeed dry between suitable rollers.

dry toner particles thereto andthe toner thereafter transferred to a record medium to produce a copy of I the original are well-known, (the Xerographic process). Such apparatus, in the useof dry toner require fusing steps to permanently affix the toner to the record member, expensive mechanisms to clean the photoc'onfor their successful operation.

A DESCRIPTION OF THE 'DRAWI N GS In theaccompanyingjdrawings formingipart hereof, similar parts have been given identical reference numerals, in which drawings: 4 I I 5 FIG; 1 is a somewhat diagrammaticside view of one complete embodiment of the presentinvention.

.ductive surfaces following each cycle and high voltages Toning an electrostatic latent image in the nip of two rollers orbetween a roller and a fla't plate or two flat plates pressed together has been disclosed in US. Pat. No. 3,556,784 issued to Robinson et al. This patent, however, requires that toning be effected simultaneously with the application of the pressure applied to the two sheets and that no toner other than that necessary to form a visible image'get pastthe line of pressure. These requirements place greatlimitations upon the nature of the equipment and supplies which can be employed in the practice of the invention.

. Accordingly, it-is an object of the present inventionto provide electrostatic printing devices free of many of the limitations of prior art devices.

Another object of the presentinven'tion is to provide,

an electrostatic printing device in' which an inexpensive recordmember is employed.

A further object of the present invention is to provide A 'FIG. 2.is a diagrammatic side vi'ew on an elongated scale showing the induction charging station of the-embodiment of FIG. 1. 7

' .FIG. 3 is a view similar to FIG. 2 showing structure for drying the record member andlatent an alternate image bearing membe'rrfollowing inductiontoning.

FIG. 4 is a somewhat diagrammatic side view of a second embodiment of the present invention employing a drum as thelatent image bearing member.

' 1 and 2; '10 indicates, somewhat diagrammatically, a

a relativelysimple and less-expensive electrostatic printing device.

Still another object of thepresent invention is to provide an electrostatic printingdevice in which the toning step is carried out between the source of electrostatic charges and the record member in the presence of an. image inducing field, I

SUMMARY. OF-THE INVENTION In the present invention a latent electrostatic-image is produced upon a sheet, plate or drum by any of the so that the gap between the record'member and the latent image bearing member is filled by the liquid toner. The record material and the latent image bearing member with the toner between them are kept in this position for an interv al'of time-sufficientfor thef eld lines emanating from the latent image to induce a mirror image of opposite sign in the record member. During this interval the field lines repelthe tonerparticles in latent image charge) thereby driving them on to the 'record member, the induced image of which attracts them thereby forming a visible image onthe record sideview of an electrostatic printing apparatus according to the present invention. It will be understood that the apparatus is enclosed in a lighttight housing 57 in accordance with well-known electrostatic printingma- I chine .principles. ,For the' purpose ofaillustration the. electrostatic image bearing member ll is shown as an elongated websuch as a strip of paper, fplastic or the like having a c'oating'l2'on o'ne facethe'reof consisting of a layer of conductive material suchas a conductive salt or resin'upon which'there is'deposited a ph'o'toconductor. The photoconductor may bea zinc-oxide in resin xerographic coating, a selenim xerographic or an organic photoconductivecoating or any of the other photoconductive materials well-known in the electrostatic printing art.' Alternately, a highly insulative 45 material may be employed for the electrostatic image bearing member in which case an electr ostatic la tent image may' be placed-thereon by-means wellknown in the art, such as anarray of charge emitter pins or the like.

The web 11 is carried as a roll 13 upon a shaft 14. After passing through theapparatus' the web 11 is wound upon a second shaft 15. I A continuous feed belt 16 is carried upon pulleys 17, 18v which are driven by a source of rotaryspower (not shown). The indicia bearing shet, indicated by the arrow 19 is fed into the nip .20 between a roller 21 and the belt-l6 with the side 'to be copied facing up. Other sheet advancing means such as rollers may also be em-- ployed.

.As the indicia sheet moves into the apparatus 10 it t'ripsa switch 22 which sets the copying mechanism in motion. The web 11 is advancedin front of a corona charger 24 or other source of ions so that a uniform electrostatic charge is placed .upon the-.photoconductive surface 12 of the web. The -,web 11 .isfurther ad-' vanced into the nip 23 formed by the feed belt l6upon the pulley l8-and a transparent or transluscent drum The indicia bearing sheet'mates with the web 11 in DEscRIPTIo oF THE PREFERRED" Y found desireable to incline the web upward slightly as shown in FIGS. 1 and 2.

A supply of record members 28 in sheet or roll form is contained within a storage chamber 28A. The record member material is selected from among ordinary papers having some barrier to liquid toner penetration as for example: clay coated, starch coated or resin coated papers. Dense sheets which have been fibrilated and calendaredduring manufacture such as glassine sheets can be used in the practice of the present invention.

Using paper as the record member-having a mosture content equilibrated to relative ambient humidities offrom percent to 90 percent or other suitable materials having resistivities of from that of conductive metals up to 1X10 ohm cms. Satisfactory copy can be achieved with machine speeds of from less than 1 to about 30 inches-per second.

The record member 28 passes across a reservoir 34 having a roller 32 which is rotated within a quantity of liquid toner 33. The toner contains particles having a charge of the same electricalsign as the latent charge image. This device, known as a kiss roller, applies a thin, uniform film of liquid-toner to the bottom surface of the record member. It is important in securing good toning and therefore satisfactory imaging that the toner liquid be first applied to the record member and not to the eletrostatically charged surface. As the two faces It will be seen from an examination of the enlarged drawing of the toning portion of the apparatus shown in FIG. 2, that the record member sheet 28 and the web 11 are brought close together by reason of the relative spacing of the rollers 31 and 35. A separation of between one-sixteenth to one-eighth inch at the rollers 31, 35 between the record member sheet 28 and the web 11 has been found suitable. The slight incline of the record member sheet material 28 and the web 11 as they' synchronously move together toward the squeege rollers 36, 37 causes the toner to flow across the opposed faces and improves the; uniformity of the toner liquid layer between the web and'record member. As shown in FIG. 2, an induced charge of opposite sign (positive) builds upupon the record member caused by the proximity of the latent charge on the photoconductivelayer 12. The field lines coming from the photoconductor'lZ pass through the toner, normal to the surface of the record member 28, thereby providing great field strength. A high contrast system result may thus beachieved in a low charge system with excellent solid areafill in. Y I In conventional liquid toning of a zinc oxide latent image bearing surface, a typical charge of 400 volts on v a coating of 20 lbs. per 3,000 squarefeet is required to produce image densities between 0.5 to 0.7. With the present invention, it is possible to achieve similar densities on the record member with zinc oxide latent image charges of volts and only 9; lbs per 3,000 square feet of zinc oxide and resin coating. As 'a result substantial economies can be achieved. Since the zinc oxide bearing web is not the final copy, less expensive base material can be used and dying of the zinc oxide resin coating to achieve desired appearance may be eliminated.

The time-interval required for induction toning (0f the order of from 0.1 sec. to 10sec.) serves to permint the build up of the induced charge on the record member and also allows tonerparticles to migrate laterally within the liquid and thereby increase the density of the i image produced on the record member. Excellent uniform solid area image fill is thus produced on the record member. I

The use of the induction time charge build up eliminates any need for contacting the'rear of eitherthe record member or web with conductive elements,-voltages or ground loop, (which devices may cause random field effects detrimental to good imaging), or connecting rollers to each other by biasing. Y

The distance between rollers 31, 35 and the squeege rollers 36, 37' provides for a charge build up interval during which induction toning occurs. The induced charge on the record member 28 increases during this internval and the toner particles in the liquid which are of opposite signto the induced charge (e.g., negative in the example illustrated) are both repelled bythe latent image charge and attracted 'to the said induced charge.

In order to produce good imaging resolution it' is imimage charge.

By the time the record member 28 and the photoconductive web 11 reach the squeege rollers 36, 37 the toning is complete and the visible image produced on the record material. The squeege rollers 36, 37 m'erely serve to drythe record member 28 and the web 11 as they pass therethrough. In some toner formulations em- 1 material 33 therebetween. Following the induction imaging step, at which time the visible image has been tor 46 as indicated byjthe arrows 49, j As the drum '45 continues to rotate it reaches the tonproduced upon the record member 28, .the web 11 is le ad away from the record member 28 by directing it The record member 28 inthe embodiment of FIG.

continues through blotter rollers 43, 44 which dry and synchronously move the toned record member and direct it out of the. apparatus. Additional air or heat can be applied to assist drying.

Referring to FIG. 4 thereis shown another embodiment of the present invention in which the-photoconductive layer support is a cylindrical drum-45. If the drum 45 is made of conductive material a photoconductive material 46 such-as zinc oxide in a resin binder, seleneium, anthracene etc. may be coated on the surface thereof. If the drum 45 is not conductive, a thin layer of a suitable conductive material suchas metal may be interposed between the drum 45 and the photoconductive material '46. In the diagrammatic illustration of FIG. 4, the drum 45 rotates in a counter clockwise direction. inidicated by the arrow 47. v

A source of electrons such as the corona charger 48 applies a uniform charge to the photoconductive material 46 as the drum 45 is rotated in front of the corona charger. It will be understood that the apparatus of FIg. 4 .is enclosed in alight tight housing 57 and that the charging of the photoconductive material is carried out I while it is in the dark adapted state.

The charged photoconductive surface is next selectively discharged in accordance with well-known electrostatic printing techniques by either reflex exposing,

The drumi45 then movesv past the cleaning station brush 56 intothe charging station in front of the corona charger 48. I i

From the foregoing it will be seen that therehave been provided electrostatic'printing devices employing induction toning in which the visi'bile image isproduced on plain (not electrostatically coated-)rpape'r and which are not subject to the limitations of prior art devices such as humidity restriction complexity, size, etc.

Having thus .fully described the invention, what is claimed as newand desired-to be secured by Letters Patent of the United States, is:

within said housing, means to createa latent charge image uponthe latent charge image receiving member,

a'source of sheet-like record material, a source of liquid toner, means to (wet) apply a thin film of said inner to at least one major surface of the record material (with the liquid toner), feed means to bring the latent as described in connection with FIG. lor by projecting a wrong reading left to right aeriel image of the indicia to be reproduced upon the surface of the photoconducing station 50 where the record material 28 which has been pre-wetted by passing it through a tray 51 containing liquid toner 33 is brought against the selectively charged surface of the drumQ The drum 45 and record material 28 withtheliquid toner therebetween rotate together synchronously, that is without lateralor horizontal' displacement with respect to each other,ffor an image'bearing member andrecord member together in an initially gapped relationship with one wetted surfaced-of the record member facing a surface of the latent image bearing member, meansto transport the said wetted record member andlatent image bearing member synchronously and along a converging path with the liquid toner on the record member in contact with the surface of the latent image bearing member until an image is induced in the record member and a visible image is formed upon the record member by the said tonerand means adjacent the end of said converging path for separating the toned'r ecord member from the latent image bearing member.

2.An electrostatic printingapparatus according to claim 1. in which thellaten't charge image receiving member is an elongated support having aphotoconcuc- 'tive insulative layer thereon. a

3. An electrostatic printingapparatus'according. to claim'2 in which the'support isa continuous stripof flexible material having an electrically conductive surcord member 28. It will be understood that if a positive image is desired the toner particles 57 will be of the The record member 28 can then be air dried, heat dried a or squeegeed dry by the rollers 53'as desired.

' face and a layer of a photoconductive on said conductive surface; I

4. An electrostaticprinting apparatus according to claim Sinwhich thephotoconductive material is a zinc oxide in resin layer.

'5. An electrostatic printing apparatusaccording to claim 1 in which the latent image bearingmember is a highly insulative stripon a conductive backing;

6. An electrostatic printing apparatus according to claim 1 in which the latentimage bearing member is a Follwoing separation of the record material at 52,the I drum 45 is rotated past a 'heater554'where a blast of warm air dried the surface of the drum of any toner liquid which may remain on the drum; A soft rotating cylindrical drum.

7. An electrostatic printingapparatus'according to claim 6 in which the surface ofthe drum is formed of electrically conductive 'material uponlwhich there is carried a layerof photoconductive material.

8., An electrostatic printing apparatus according to claim 7 in which the photoconductive material is selenium. l

9. An electrostatic printing apparatus according to claim 6 in which the latent charge image. creating means comprises means to .uniformlycharge the charge image receiving surface of the .drum and means to 'direct anaerial image upon said uniform charge.

10. An electrostatic printing apparatus according to I claim 1 in which the feed means to bring the latent image bearing member and the record member tomater'ial' carried gether includes at least one roller closely adjacent the latent image bearingmember and disposed so as to direct the record member toward the latent image bearing member.

11. An electrostatic printing apparatus according to claim 10 in which the roller is separated from the latent image bearing surface a distance of the order of onesixteenth to one-eighth inch. I

12. An electrostatic printing apparatus according to claim 10 in which the feed means includes a pair of squeegee rollers disposed at the end of the synchronous travel path of the latent image bearing member and record member and before the separating means.

13. An electrostatic printing apparatus according to claim 12 in which the squeegee rollers are disposed on either side of the record member following the separating means. 1

14. An electrostatic printing apparatus according to claim 1 in which the transport means directs the wetted record member and the latent image bearing member upwardly and along a non-vertical path whereby the liquid toner flows, between the record member and the facing surface of the latent image bearing member.

15. An electrostatic printing apparatus according to claim 14 in which the non-vertical path is sloping.

16. An electrostatic printing apparatus according to claim 14 in which the non-vertical path is curvilinear. a: 

1. An electrostatic printing apparatus comprising a housing, a latent charge image receiving member within said housing, means to create a latent charge image upon the latent charge image receiving member, a source of sheet-like record material, a source of liquid toner, means to (wet) apply a thin film of said toner to at least one major surface of the record material (with the liquid toner), feed means to bring the latent image bearing member and record member together in an initially gapped relationship with one wetted surfaced of the record member facing a surface of the latent image bearing member, means to transport the said wetted record member and latent image bearing member synchronously and along a converging path with the liquid toner on the record member in contact with the surface of the latent image bearing member until an image is induced in the record member and a visible image is formed upon the record member by the said toner and means adjacent the end of said converging path for separating the toned record member from the latent image bearing member.
 2. An electrostatic printing apparatus according to claim 1 in which the latent charge image receiving member is an elongated support having a photoconcuctive insulative layer thereon.
 3. An electrostatic printing apparatus according to claim 2 in which the support is a continuous strip of flexible material having an electrically conductive surface and a layer of a photoconductive material carried on said conductive surface.
 4. An electrostatic printing apparatus according to claim 3 in which the pHotoconductive material is a zinc oxide in resin layer.
 5. An electrostatic printing apparatus according to claim 1 in which the latent image bearing member is a highly insulative strip on a conductive backing.
 6. An electrostatic printing apparatus according to claim 1 in which the latent image bearing member is a cylindrical drum.
 7. An electrostatic printing apparatus according to claim 6 in which the surface of the drum is formed of electrically conductive material upon which there is carried a layer of photoconductive material.
 8. An electrostatic printing apparatus according to claim 7 in which the photoconductive material is selenium.
 9. An electrostatic printing apparatus according to claim 6 in which the latent charge image creating means comprises means to uniformly charge the charge image receiving surface of the drum and means to direct an aerial image upon said uniform charge.
 10. An electrostatic printing apparatus according to claim 1 in which the feed means to bring the latent image bearing member and the record member together includes at least one roller closely adjacent the latent image bearing member and disposed so as to direct the record member toward the latent image bearing member.
 11. An electrostatic printing apparatus according to claim 10 in which the roller is separated from the latent image bearing surface a distance of the order of one-sixteenth to one-eighth inch.
 12. An electrostatic printing apparatus according to claim 10 in which the feed means includes a pair of squeegee rollers disposed at the end of the synchronous travel path of the latent image bearing member and record member and before the separating means.
 13. An electrostatic printing apparatus according to claim 12 in which the squeegee rollers are disposed on either side of the record member following the separating means.
 14. An electrostatic printing apparatus according to claim 1 in which the transport means directs the wetted record member and the latent image bearing member upwardly and along a non-vertical path whereby the liquid toner flows, between the record member and the facing surface of the latent image bearing member.
 15. An electrostatic printing apparatus according to claim 14 in which the non-vertical path is sloping.
 16. An electrostatic printing apparatus according to claim 14 in which the non-vertical path is curvilinear. 